Kalani read a letter to his stepdad, thanking him for everything he has done. The touching moment was captured on video by Kalani's mother and Williamson's wife, Porsche, and the Facebook post has since gone viral.

“So let’s stop playing and make it official,” Kalani says to his stepfather. “Will you do me the biggest favor in the world? Will you adopt me?”

That’s when Williamson, who appeared to be holding back tears, broke down and the two embraced.

Kalani then gave his stepfather a wrapped box. The official adoption papers were inside.

"I can't watch the video," Williamson said. "It still chokes me up."

Porsche Williamson, Kalani's mother, said the birthday surprise took about two months to plan.

"It felt amazing," she said about the momentous event. "I know what he feels for Brandon, but he don’t express it much."

The video, posted on April 30, has gotten 3.3 million views on Facebook and has been shared more than 57,000 times.

For Kalani, who hasn’t seen his biological father in years, Williamson is his father and has been since they met when the boy was a baby.

When he was 4, Kalani mustered up the courage to call Williamson “daddy.”

“That was another day I won’t forget,” Williamson said.

“It felt good to let everything out and tell my dad how I feel about him,” Kalani said.